Magnetic tunnel junctions suitable for high temperature thermal processing

ABSTRACT

Embodiments herein provide film stacks that include a buffer layer; a synthetic ferrimagnet (SyF) coupling layer; and a capping layer, wherein the capping layer comprises one or more layers, and wherein the capping layer, the buffer layer, the SyF coupling layer, or a combination thereof, is not fabricated from Ru.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of co-pending U.S. patent application Ser. No.16/272,183, filed Feb. 11, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/862,301, filed Jan. 4, 2018, now U.S. Pat. No.10,255,935, issued Apr. 9, 2019, which claims the benefit of U.S.Provisional Patent Application No. 62/535,792, filed Jul. 21, 2017, eachof which is incorporated by reference herein in its entirety.

FIELD

Embodiments of the present disclosure relate to methods for fabricatingstructures used in spin-transfer-torque magnetic random access memory(STT-MRAM) applications. More specifically, embodiments of thedisclosure relate to methods for fabricating magnetic tunnel junctionstructures for MRAM applications.

BACKGROUND

Magnetic random access memory (MRAM) is a type of memory devicecontaining an array of MRAM cells that store data using their resistancevalues instead of electronic charges. Generally, each MRAM cell includesa magnetic tunnel junction (MTJ) structure. The MTJ structure typicallyincludes a stack of magnetic layers having a configuration in which twoferromagnetic layers are separated by a thin non-magnetic dielectric,e.g., an insulating tunneling layer. A top electrode and a bottomelectrode are utilized to sandwich the MTJ structure so electric currentmay flow between the top and the bottom electrode.

One type of MRAM cell is spin-transfer-torque magnetic random accessmemory (STT-MRAM). In such a fabrication process flow, a stable magnetictunnel junction (MTJ) stack is needed to sustain high temperaturebackend thermal processing while still producing high tunnelmagnetoresistance (TMR) ratio. MTJ stack often starts with a bufferlayer to improve adhesion and the seeding of the subsequent layers. MTJstack also includes a synthetic ferrimagnet (SyF) coupling layer tocouple the first pinning layer and the second pinning layerantiparallelly. A capping layer is utilized on top of the MTJ stack thatends with a noble metal material, which protects the stack fromcorrosion and also acts as a etch stop layer for hard mask etching.

During manufacturing of conventional STT-MRAM devices, a thermalannealing process is often performed right after the film layerdeposition process to assist crystallization of the ferromagnetic layersas well as the insulator material sandwiched in the device structure.Insufficient thermal energy or inaccurate temperature control during theannealing process may cause the film bonding structures or propertiesformed in an undesirable manner. For example, inaccurate temperaturecontrol or undesired drift of the thermal diffusion during the annealingprocess may result in insufficient crystallization of the film layer,leading to failure of the device to meet its intended performance.

Conventional methods use a Ta- and/or Ru-based buffer layer for purposesadhesion and seeding of the subsequent layers. However, the buffer layeris easy to be segregated. The texture from the bottom contact tends toaffect the texture of the MTJ film stack through the buffer and becomesdetrimental to TMR ratio and magnetic properties of the stack, i.e., thetexture roughness is carried from the substrate/bottom contact layers tothe other layers of the MTJ film stack. Ru is also used in conventionalmethods for fabricating SyF coupling layers and capping layers. However,Ru tends to diffuse towards the MgO based tunnel barrier layer to bondwith oxygen ion. Such detrimental diffusion lowers the TMR ratio of thefilm stack. The effect becomes severe during thermal process at elevatedtemperatures.

Therefore, there is a need in the art for improved methods and apparatusfor fabricating MTJ structures for STT-MRAM applications with highvolume manufacturability. There is also a need for improved MTJ stacksthat are able to sustain high temperature thermal processing whilepreserving high TMR ratio and magnetic properties such as high SyFcoupling, high perpendicular magnetic anisotropy of pinned layers andreference layer, and controllable perpendicular magnetic anisotropy offree layer.

SUMMARY

Embodiments of the disclosure provide methods for fabricating magnetictunnel junction (MTJ) structures on a substrate in MRAM applications,particularly for spin-transfer-torque magnetic random access memory(STT-MRAM) applications. Some embodiments provide compositions of filmstacks for MTJ structures.

In an embodiment, a film stack is provided that includes a buffer layer;a synthetic ferrimagnet (SyF) coupling layer; and a capping layer,wherein the capping layer comprises one or more layers, and wherein thecapping layer, the buffer layer, the SyF coupling layer, or acombination thereof, is not fabricated from Ru.

In another embodiment, a film stack is provided that includes a bufferlayer, wherein the buffer layer comprises a CoFeB containing layer; asynthetic ferrimagnet (SyF) coupling layer, the SyF coupling layercomprising an Ir containing layer; and a capping layer, wherein thecapping layer comprising one or more layers, and wherein the cappinglayer, the buffer layer, the SyF coupling layer, or a combinationthereof, is not fabricated from Ru.

In another embodiment, a film stack is provided that includes a bufferlayer, wherein the buffer layer comprises a CoFeB containing layer,wherein a wt % of boron is greater than about 20%; a syntheticferrimagnet (SyF) coupling layer, the SyF coupling layer comprising anIr containing layer; and a capping layer, wherein the capping layercomprises one or more layers, wherein a top layer of the capping layeris an Ir containing layer, and wherein the capping layer, the bufferlayer, the SyF coupling layer, or a combination thereof, is notfabricated from Ru

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, and may admit to other equally effective embodiments.

FIG. 1 depicts a flow diagram illustrating a method for fabricatingmagnetic tunnel junction (MTJ) structures, according to someembodiments.

FIG. 2A shows a schematic diagram of a portion of a film stack,according to some embodiments.

FIG. 2B shows a schematic diagram of a portion of the film stack,according to some embodiments.

FIG. 2C shows a schematic diagram of a portion of the film stack,according to some embodiments.

FIG. 3A shows a schematic diagram of a capping layer, according to someembodiments.

FIG. 3B shows a schematic diagram of a capping layer, according to someembodiments.

FIG. 3C shows a schematic diagram of a capping layer, according to someembodiments.

FIG. 3D shows a schematic diagram of a capping layer, according to someembodiments.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this disclosure and aretherefore not to be considered limiting of its scope, for the disclosuremay admit to other equally effective embodiments.

DETAILED DESCRIPTION

Embodiments of the disclosure generally provide apparatus and methodsfor forming MTJ structures from a film stack disposed on a substrate forMRAM applications. The apparatus and methods include forming the filmproperties of material layers from the film stack with desiredcrystallinity by a thermal process performed after the patterning of thematerial layers in the film stack. While patterning, a sidewallpassivation layer may be formed along sidewalls of the film stack. Thus,by performing the thermal process after the patterning process and thesidewall passivation deposition process, the thermal energy providedfrom the thermal process may efficiency diffuse dopants into thematerial layers laterally outward toward the sidewall passivation layer,rather than vertically to adjacent material layers formed in the filmstack. By doing so, a controllable degree of crystallinity of thematerial layers in the film stack may be obtained without damage orinterference from the dopants that might potentially be cross-diffusedfrom the adjacent materials. The film stack as patterned and annealedwith desired degree of crystallinity may be used to form MTJ structureswith desired dimension and features for MRAM applications.

FIG. 1 depicts a flow diagram illustrating a process 100 formanufacturing MTJ structures on a substrate for MRAM applicationsaccording to one embodiment of the present disclosure. In someembodiments, process 100 is a process flow, and operations 101-106 areindividual processes. The process 100 is configured to be performed in aplasma processing chamber and a thermal processing chamber or othersuitable plasma immersion ion implantation systems or etching chamber,including those from other manufacturers. Process 100 may also use othertools such as a PVD chamber, CVD chamber, lithography tool.

The process 100 begins at operation 101 by providing a substrate havinga film stack disposed thereon. In some embodiments, the substrateincludes metal or glass, silicon, dielectric bulk material and metalalloys or composite glass, crystalline silicon (e.g., Si<100> orSi<111>), silicon oxide, strained silicon, silicon germanium, germanium,doped or undoped polysilicon, doped or undoped silicon wafers andpatterned or non-patterned wafers silicon on insulator (SOI), carbondoped silicon oxides, silicon nitride, doped silicon, germanium, galliumarsenide, glass, or sapphire. The substrate may have various dimensions,such as about 200 mm, about 300 mm, about 450 mm or other diameter, aswell as, being a rectangular or square panel. Unless otherwise noted,examples described herein are conducted on substrates with a 200 mmdiameter, a 300 mm diameter, or a 450 mm diameter substrate. In oneembodiment, the substrate includes the film stack disposed on thesubstrate.

It is noted that pinned magnetic layer(s), optional structure decouplinglayer(s), tunnel barrier layer(s), magnetic storage layer(s), magneticreference layer(s), and capping layer(s) may be formed by any suitabletechniques and any suitable manners, such as PVD processes. Examples ofsystems that may be used to form these layers include ENDURA® PVD systemavailable from Applied Materials Inc., Santa Clara, Calif. It iscontemplated that other processing system, including those availablefrom other manufacturers, may be adapted to practice the disclosure.

Prior to performing MTJ stack deposition at operation 102, there may besome other processes to form transistor and interconnect layers, knownto those of skill in the art. After performing a post-patterning annealat operation 106, additional operations may be performed, such asoperations to complete remaining interconnect layers and contact pads.

At operations 102-104, MTJ stack deposition, pre-patterning anneal, andMTJ patterning is performed. These operations include a patterningprocess, e.g., an etching process, performed to remove a portion of thefilm stack exposed and defined by an etching mask layer (not shown) fromthe substrate until the underlying substrate is exposed. The patterningprocess for patterning the film stack may include several steps ordifferent recipes configured to supply different gas mixtures oretchants to etch different layers in accordance with the materialsincluded in each layer. During patterning, an etching gas mixture orseveral gas mixtures with different etching species are sequentiallysupplied into the substrate surface to remove the portion of the filmstack from the substrate. The end point of the patterning process atoperation 104 may be controlled by time or other suitable methods. Forexample, the patterning process may be terminated after performing forbetween about 200 seconds and about 10 minutes until the substrate isexposed. The patterning process may be terminated by determination froman endpoint detector, such as an OES detector or other suitable detectoras needed.

A further deposition process may be performed to form an encapsulationand insulation layer on the portion of the substrate where the filmstack was removed during the pattering process at operation 104.Encapsulation allows for good step coverage and hermeticity, and isoften composed of silicon nitride based materials. Insulation is oftencomposed of oxide based materials, and typically much thicker thanencapsulation. The insulation layer may be any suitable insulatingmaterials that may later under series of etching and depositionprocesses to form interconnection structure (e.g., a backend process) inthe insulation layer to complete the device structure fabricationprocess. In one example, the insulation layer is a silicon oxide layeror other suitable material.

At operation 106, a thermal annealing process is performed. One exampleof a system that may be used for annealing includes rapid thermal annealchambers available from Applied Materials Inc., Santa Clara, Calif. Itis contemplated that other processing system, including those availablefrom other manufacturers, may be adapted to practice the disclosure. Thethermal annealing process is performed to repair, densify and enhancelattice structures of the film stack, particularly the magnetic storagelayer(s) and the magnetic reference layer(s) included in the film stack.After the thermal annealing process, the magnetic storage layer(s) andmagnetic reference layer(s) may be turned into a crystallized magneticstorage layer(s) and crystallized magnetic reference layer(s), havingcrystal orientation mostly in one plane. As desired crystallization ofthe magnetic storage layer(s) and the magnetic reference layer(s) isobtained, the overall electrical properties of the film stack formanufacturing MTJ devices are improved.

In some embodiments, one of operations 103 and 106 (or any otherequivalent anneal process) can be used, depending on applications.

As described below, the MTJ film stacks of the present disclosure arecapable of sustaining high temperature thermal processes and improvedelectrical and magnetic properties.

Each of FIGS. 2A-2C individually show a schematic diagram of a portionof the film stack, according to some embodiments. 200 is a substrate.204 is a bottom electrode, which is patterned in some embodiments.Although not depicted in FIGS. 2A-2C, other layers such as transistorand interconnect structures in the form of one or more layers may bedisposed between substrate 200 and bottom contact 204 according to someembodiments. Differences between film stacks illustrated in FIG. 2B andFIG. 2C include the buffer layer 205/205′, seed layer 210/210′, andfirst pinning layer 215/215′. In some embodiments, a film stack includesone or more of a bottom contact, a buffer layer, a seed layer, a firstpinning layer, a synthetic ferrimagnet (SyF) coupling layer, a secondpinning layer, a structure blocking layer, a magnetic reference layer, atunnel barrier layer, a magnetic storage layer, a capping layer, and ahard mask. In some embodiments, each of these layers individuallycomprises one or more layers.

In some embodiments, and as shown in FIG. 2A-2C, the film stack utilizedto form a magnetic tunnel junction (MTJ) structure is disposed over abottom contact 204. The MTJ structure includes a buffer layer 205/205′disposed over the bottom contact 204; a seed layer 210/210′ disposedover the buffer layer 205/205′; a first pinning layer 215/215′ disposedover the seed layer 210/210′; a synthetic ferrimagnet (SyF) couplinglayer 220 disposed over the first pinning layer 215/215′; a secondpinning layer 225 disposed over the SyF coupling layer 220; a structureblocking layer 230 disposed over the second pinning layer 225; amagnetic reference layer 235 disposed over the structure blocking layer230; a tunnel barrier layer 240 disposed over the magnetic referencelayer 235; a magnetic storage layer 245 disposed over the tunnel barrierlayer 240; a capping layer 250 disposed over the magnetic storage layer245, wherein the capping layer includes one or more layers; and a hardmask 255 disposed over the capping layer 250, wherein at least one ofthe capping layer, the buffer layer, and the SyF coupling layer is notfabricated from Ru.

The film stack includes a buffer layer 205/205′ disposed over a bottomcontact 204. The buffer layer 205/205′ may be sandwiched between bottomcontact 204 and seed layer 210/210′. MTJ film stacks often start with abuffer layer to improve adhesion and the seeding of the subsequentlayers. In some embodiments, buffer layer 205/205′ includes one or morelayers. In some embodiments, the buffer layer is not fabricated from Ru.

In some embodiments, the buffer layer includes a CoFeB containing layer205 a/205 a′. The weight % (wt %) of boron (B) in the buffer layer cisbetween about 10 wt % and about 40 wt %, preferably between about 20 wt% and 40 wt %, more preferably between about 25 wt % and about 40 wt %.The wt % of iron in the buffer layer is between about 20 wt % and about60 wt %, preferably between about 40 wt % and 60 wt %, more preferablybetween about 45 wt % and about 60 wt %. The thickness of the CoFeBcontaining layer 205 a/205 a′ is between about 0 Å and about 20 Å,preferably about 10 Å.

In some embodiments, the buffer layer 205/205′ may comprise a TaNcontaining layer 205 b/205 b′ and/or a Ta containing layer 205 c/205 c′.The TaN containing layer 205 b/205 b′ and the Ta containing layer 205c/205 c′ may be disposed over the CoFeB layer. Alternately, the TaNcontaining layer 205 b/205 b′ and the Ta containing layer 205 c/205 c′may be disposed under the CoFeB layer. The thickness of the TaNcontaining layer and the Ta containing layer is between about 0 Å andabout 40 Å, preferably about 15 Å.

The film stack includes a seed layer 210/210′ disposed over the bufferlayer 205/205′. The seed layer 210/210′ may be sandwiched between thebuffer layer 205/205′ and first pinning layer 215/215′.

In some embodiments, seed layer 210 includes one or more of a Ptcontaining layer, an Ir containing layer, and a Ru containing layer. Thethickness of seed layer 210 having one or more of Pt containing layer,an Ir containing layer, and a Ru containing layer is between about 0 Åand about 60 Å, preferably about 25 Å. In some embodiments, when theseed layer 210 includes one or more of a Pt containing layer, an Ircontaining layer, and a Ru containing layer, the CoFeB containing layer205 a of the buffer layer is disposed under the TaN containing layer 205b (and/or Ta containing layer 205 c) of the buffer layer.

In some embodiments, seed layer 210′ includes a NiCr containing layer.The thickness of seed layer 210′ having a NiCr containing layer isbetween about 0 Å and about 100 Å, preferably about 50 Å. In someembodiments, when the seed layer includes a NiCr containing layer, theCoFeB containing layer 205 a′ of the buffer layer is disposed over theTaN containing layer 205 b′ (and/or Ta containing layer 205 c′) of thebuffer layer.

In some embodiments, the film stack includes a first pinning layer215/215′ disposed over seed layer 210/210′. The first pinning layer215/215′ may be sandwiched between seed layer 210/210′ and SyF couplinglayer 220. The first pinning layer 215/215′ may comprise one or morelayers. The first pinning layer may be constructed of several magneticmaterials such as a metal alloy with dopants, such as boron dopants,oxygen dopants or other suitable materials. Metal alloys may include aNi containing material, a Pt containing material, a Ru containingmaterial, a Co containing material, a Ta containing material, and Pdcontaining materials. Suitable examples of the magnetic materialsinclude Ru, Ta, Co, Pt, Ni, TaN, NiFeO_(x), NiFeB, CoFeO_(x)B, CoFeB,CoFe, NiO_(x)B, CoBO_(x), FeBO_(x), CoFeNiB, CoPt, CoPd, CoNi, andTaO_(x).

In some embodiments, first pinning layer 215 includes a Co containinglayer 215 b disposed over a Co/Pt containing layer 215 a. The thicknessof the Co containing layer 215 b is between about 0 Å and about 10 Å,preferably about 5 Å. The Co/Pt containing layer 215 a may have acomposition comprising

[CO_((x))/Pt_((y))]_(m)

wherein x has a thickness of Co between about 0 Å and about 10 Å,preferably between about 0.5 Å and about 7 Å, y has a thickness of Ptbetween about 0 Å and about 10 Å, preferably between about 0.5 Å andabout 8 Å, and m is an integer between about 3 and about 10, wherein mrepresents the number of Co/Pt containing layers 215 a repeatedly formedin the film stack. For example, when x is 5 Å, y is 3 Å, and m isinteger 2, it represents a Co/Pt layer of Co layer (5 Å)/Pt layer (3Å)/Co layer (5 Å)/Pt layer (3 Å).

In some embodiments, first pinning layer 215′ includes a Co containinglayer 215 b′ disposed over a Co/Ni containing layer 215 a′. Thethickness of the Co containing layer 215 b is between about 0 Å andabout 10 Å, preferably about 5 Å. The Co/Ni containing layer 215 a′ mayhave a composition comprising

[Co_((x1))/Ni_((y1))]_(n)

wherein x1 has a thickness of Co between about 0 Å and about 10 Å,preferably between about 1 Å and about 8 Å, y1 has a thickness of Nibetween about 0 Å and about 10 Å, preferably between about 1 Å and about8 Å, and n is an integer between about 1 and about 10, where nrepresents the number of Co/Ni containing layers 215 a′ repeatedlyformed in the film stack.

In some embodiments, when the first pinning layer 215 includes Co/Ptcontaining layer 215 a, the seed layer 210 includes one or more of a Ptcontaining layer, an Ir containing layer, and a Ru containing layer.

In some embodiments, when the first pinning layer 215′ includes a Co/Nicontaining layer 215 a′, the seed layer 210 includes a NiCr containinglayer.

The film stack includes a synthetic ferrimagnet (SyF) coupling layer 220disposed over the first pinning layer 215/215′. In some embodiments, theSyF coupling layer 220 is sandwiched between first pinning layer215/215′ and second pinning layer 225. The SyF coupling layer 220 isused to couple the first pinning layer and the second pinning layerantiparallely. In some embodiments, the SyF coupling layer 220 includesone or more of an Ir containing layer, a Ru containing layer, a Rhcontaining layer, and a Cr containing layer. Preferably the SyF couplinglayer is an Ir containing layer. Preferably, the SyF coupling layer isnot fabricated from Ru. The thickness of SyF coupling layer 220 isbetween about 3 Å and about 10 Å. When the SyF coupling layer is a Rucontaining layer, the thickness of the layer is preferably between about4 Å and about 5 Å or between about 7 Å and about 9 Å. When the SyFcoupling layer is an Ir containing layer, the thickness of the layer ispreferably between about 4 Å and about 6 Å.

The film stack includes a second pinning layer 225 disposed over SyFcoupling layer 220. In some embodiments, the second pinning layer 225 issandwiched between SyF coupling layer 220 and structure blocking layer230. The second pinning layer 225 may comprise one or more layers. Thesecond pinning layer may be constructed of several magnetic materialssuch as a metal alloy with dopants, such as boron dopants, oxygendopants or other suitable materials. Metal alloys may include a Nicontaining material, a Pt containing material, a Ru containing material,a Co containing material, a Ta containing material, and Pd containingmaterials. Suitable examples of the magnetic materials include Ru, Ta,Co, Pt, Ni, TaN, NiFeO_(x), NiFeB, CoFeO_(x)B, CoFeB, CoFe, NiO_(x)B,CoBO_(x), FeBO_(x), CoFeNiB, CoPt, CoPd, CoNi, and TaO_(x).

In some embodiments, second pinning layer 225 includes a Co containinglayer 225 b disposed over a Co/Pt containing layer 215 a. The thicknessof the Co containing layer 225 b is between about 0 Å and about 10 Å,preferably about 5 Å. The Co/Pt containing layer 215 a may have acomposition comprising

[Co_((x2))/Pt_((y2))]_(p)

wherein x2 has a thickness of Co between about 0 Å and about 10 Å,preferably between about 0.5 Å and about 7 Å, y2 has a thickness of Ptbetween about 0 Å and about 10 Å, preferably between about 0.5 Å andabout 8 Å, and p is an integer between about 0 and about 5, where prepresents the number of Co/Pt containing layers 225 a repeatedly formedin the film stack.

The film stack includes structure blocking layer 230 disposed oversecond pinning layer 225. In some embodiments, structure blocking layer230 is sandwiched between second pinning layer 225 and magneticreference layer 235. In some embodiments, structure blocking layer 230includes one or more layers. In some embodiments, the structure blockinglayer 230 includes one or more of a metal containing material or amagnetic material, such as Mo, Ta, W, CoFe, and CoFeB, preferably one ormore of a Ta containing layer, a Mo containing layer, and a W containinglayer. The thickness of second pinning layer 225 is between about 0 Åand about 8 Å, preferably about 4 Å.

The film stack includes a magnetic reference layer 235 disposed over astructure blocking layer 230. In some embodiments, magnetic referencelayer 235 is sandwiched between structure blocking layer 230 and tunnelbarrier layer 240. In some embodiments, the magnetic reference layer 235comprises one or more layers. Magnetic reference layer 235 may beconstructed of several magnetic materials such as a metal alloy withdopants, such as boron dopants, oxygen dopants or other suitablematerials. Metal alloys may include a Ni containing material, a Ptcontaining material, a Ru containing material, a Co containing material,a Ta containing material, and Pd containing materials. Suitable examplesof the magnetic materials include Ru, Ta, Co, Pt, Ni, TaN, NiFeO_(x),NiFeB, CoFeO_(x)B, CoFeB, CoFe, NiO_(x)B, CoBO_(x), FeBO_(x), CoFeNiB,CoPt, CoPd, CoNi, and TaO_(x).

In some embodiments, one or more of the layers of the magnetic referencelayer 235 includes a CoFeB containing layer. The weight % (wt %) ofboron (B) in the magnetic reference layer is between about 10 wt % andabout 40 wt %, preferably between about 20 wt % and 40 wt %, morepreferably between about 25 wt % and about 40 wt %. The wt % of iron inthe magnetic reference layer is between about 20 wt % and about 60 wt %,preferably between about 40 wt % and 60 wt %, more preferably betweenabout 45 wt % and about 60 wt %. The thickness of the magnetic referencelayer 235 is between about 5 Å and about 20 Å, preferably about 10 Å.

In some embodiments, the film stack includes a tunnel barrier layer 240disposed over magnetic reference layer 235. In some embodiments, tunnelbarrier layer 240 is sandwiched between magnetic reference layer 235 andmagnetic storage layer 245. Tunnel barrier layer 240 may be an oxidebarrier layer. The tunnel barrier layer 240 may include MgO, HfO₂, TiO₂,TaO_(x), Al₂O₃, or other suitable materials. In some embodiments, thetunnel barrier layer 240 may comprise MgO having a thickness of betweenabout 1 Å and about 15 Å, preferably about 10 Å. The tunnel barrierlayer 240 may be annealed either during or post deposition, for example,using a rapid thermal anneal (RTP) process.

In some embodiments, the film stack includes a magnetic storage layer245 disposed over tunnel barrier layer 240. In some embodiments,magnetic storage layer 245 is sandwiched between tunnel barrier layer240 and capping layer 250. The magnetic storage layer 245 may beconstructed of several magnetic materials such as a metal alloy withdopants, such as boron dopants, oxygen dopants or other suitablematerials. Metal alloys may include a Ni containing material, a Ptcontaining material, a Ru containing material, a Co containing material,a Ta containing material, and/or Pd containing materials. Suitableexamples of the magnetic materials include Ru, Ta, Co, Pt, Ni, TaN,NiFeO_(x), NiFeB, CoFeO_(x)B, CoFeB, CoFe, NiO_(x)B, CoBO_(x), FeBO_(x),CoFeNiB, CoPt, CoPd, CoNi, and TaO_(x).

In some embodiments, magnetic storage layer 245 may be a CoFeB, CoFeNiB,Ta, Mo or W, combinations thereof or other suitable layer(s). Forexample, in the embodiment depicted in FIG. 2, the magnetic storagelayer 245 includes a first CoFeB containing layer 245 a and a secondCoFeB containing layer 245 c sandwiching an intermediate layer 245 b.The first CoFeB containing layer 245 a may have a thickness of about 5 Åto about 20 Å, preferably about 10 Å. The weight % (wt %) of boron (B)in the first CoFeB containing layer 245 a is between about 10 wt % andabout 40 wt %, preferably between about 20 wt % and 40 wt %, morepreferably between about 25 wt % and about 40 wt %. The wt % of iron inthe first CoFeB containing layer 245 a is between about 20 wt % andabout 60 wt %, preferably between about 40 wt % and 60 wt %, morepreferably between about 45 wt % and about 60 wt %.

The second CoFeB containing layer 245 c may have a thickness of about 5Å to about 20 Å, preferably about 10 Å. The weight % (wt %) of boron (B)in the second CoFeB containing layer 245 c is between about 10 wt % andabout 40 wt %, preferably between about 20 wt % and 40 wt %, morepreferably between about 25 wt % and about 40 wt %. The wt % of iron inthe second CoFeB containing layer 245 a is between about 20 wt % andabout 60 wt %, preferably between about 40 wt % and 60 wt %, morepreferably between about 45 wt % and about 60 wt %.

The intermediate layer 245 b of the magnetic storage layer 245 mayinclude one or more layers of at least one or more of a Ta containinglayer, a Mo containing layer, and a W containing layer. The intermediatelayer 245 b may have a thickness of about 0 Å to about 8 Å, for exampleabout 3 Å.

The film stack includes capping layer 250 disposed over magnetic storagelayer 245. In some embodiments, capping layer 250 is sandwiched betweenmagnetic storage layer 245 and hard mask 255. A capping layer isutilized on top of the MTJ stack that ends with a noble metal material,which protects the stack from corrosion and also acts as a etch stoplayer for hard mask etching. In some embodiments, capping layer 250includes one or more layers.

In some embodiments, the capping layer 250 includes a first layer 250 a,a second layer 250 b, a third layer 250 c, and a fourth layer 250 d.

The first layer 250 a may include one or more layers of oxygencontaining layers such as MgO or other suitable materials. Preferably,the oxygen containing layer is MgO. The first layer 250 a may have athickness of between about 0 Å to about 15 Å, for example about 7 Å. Thesecond layer 250 b may include one or more layers of CoFeB. The secondlayer 250 b may have a thickness of between about 0 Å to about 50 Å, forexample about 8 Å. The weight % (wt %) of boron (B) of second layer 250b is between about 10 wt % and about 40 wt %, preferably between about20 wt % and 40 wt %, more preferably between about 25 wt % and about 40wt %. The wt % of iron in second layer 250 b is between about 20 wt %and about 60 wt %, preferably between about 40 wt % and 60 wt %, morepreferably between about 45 wt % and about 60 wt %.

The third layer 250 c may include one or more layers of a Ta containingmaterial. The third layer 250 c may have a thickness of between about 0Å to about 30 Å, for example about 10 Å. The fourth layer 250 d mayinclude one or more of an Ir containing layer and a Ru containing layer,preferably one or more of an Ir containing layer. The fourth layer 250 dmay have a thickness of between about 0 Å to about 50 Å, for exampleabout 30 Å.

In some embodiments, the one or more layers of capping layer 250 includeone or more layers of an Ir containing layer, one or more layers of a Rucontaining layer, or a combination thereof.

In some embodiments, the one or more layers of capping layer 250 includeone or more of an Ir containing layer, a Ru containing layer, a Tacontaining layer, a CoFeB containing layer, an Mo containing layer, a Wcontaining layer, and a oxygen containing layer (for example, MgO).Preferably an Ir containing layer or an Ru containing layer (morepreferably an Ir containing layer) is the top layer of the capping layeras the hard mask etch stop. In some embodiments, the capping layer isnot fabricated from Ru.

In some embodiments, the capping layer includes an optional layer 250 x.Optional layer may be disposed between the first layer 250 a and thesecond layer 250 b. The optional layer 250 x, may include one or morelayers of a Ir containing layer and/or a Ru containing layer, preferablyIr. Optional layer 250 x may have a thickness of between about 0 Å toabout 30 Å, for example about 20 Å.

In some embodiments, when the capping layer 250 includes optional layer250 x, second layer 250 b is not used. In such an embodiment, optionallayer 250 x is above first layer 250 a. In some embodiments, optionallayer 250 x is disposed directly above first layer 250 a. In someembodiments, additional layers may be disposed above 250 x.

In some embodiments, the capping layer comprises optional layer 250 xand first layer 250 a. In this embodiment, for example, the cappinglayer would be an Ir and/or Ru containing layer and an oxygen containinglayer, with the Ir and/or Ru containing layer above the oxygencontaining layer. In other embodiments, the capping layer includesoptional layer 250 x, first layer 250 a, and one or more of second layer250 b, third layer 250 c, and fourth layer 250 d, where optional layer250 x is disposed directly above oxygen containing layer 250 a.

FIGS. 3A-3D illustrates various, nonexclusive embodiments of the cappinglayer 250 as discussed above.

For example in FIG. 3A, capping layer 250 includes a first layer 250 a;an optional layer 250 x disposed above the first layer 250 a; a secondlayer 250 b disposed above the optional layer 250 x; a third layer 250 cdisposed above the second layer 250 b; and a fourth layer 250 d disposedabove the third layer 250 c. Materials, compositions, and thicknessranges for each of these layers are discussed above.

In the example of FIG. 3B, capping layer 250 includes a first layer 250a; a second layer 250 b disposed above the first layer 250 a; a thirdlayer 250 c disposed above the second layer 250 b; and a fourth layer250 d disposed above the third layer 250 c. Materials, compositions, andthickness ranges for each of these layers are discussed above.

In the example of FIG. 3C, capping layer 250 includes a first layer 250a; an optional layer 250 x disposed above the first layer 250 a; a thirdlayer 250 c disposed above the optional layer 250 x; and a fourth layer250 d disposed above the third layer 250 c. Materials, compositions, andthickness ranges for each of these layers are discussed above.

In the example of FIG. 3C, capping layer 250 includes a first layer 250a; and an optional layer 250 x disposed above the first layer 250 a.Materials, compositions, and thickness ranges for each of these layersare discussed above.

FIGS. 2A-2C illustrate exemplary MTJ film stacks wherein one or more ofthe buffer layer, the SyF coupling layer, and the capping layer is notfabricated from Ru. In some embodiments, the MTJ film stack includes aCoFeB based buffer layer 205/205′, which optionally may contain some TaNand/or Ta. The CoFeB layer may be disposed over or under a layercontaining TaN and/or Ta. The wt % of boron of the CoFeB based bufferlayer should be greater than about 10 wt %, preferably greater thanabout 25 wt %. In some embodiments, Ir, Ru, Rh, and/or Cr may be used asa SyF coupling layer 220, preferably Ir is the SyF coupling layer. Insome embodiments, Ir and/or Ru may be the top layer metal for a cappinglayer 250. Ir is preferred as the top layer metal for a capping layer250.

Use of a CoFeB based buffer layer in place of a Ru containing bufferlayer has demonstrated an increase in the tunnel magnetoresistance (TMR)with excellent magnetic pinning even after annealing at temperatures upto 450° C. High SyF coupling, high perpendicular magnetic anisotropy ofpinned layers and reference layer, and controllable perpendicularmagnetic anisotropy of free layer are achieved. Some embodimentsimplementing a CoFeB buffer layer (with boron at 25 wt %) show a TMR (%)improvement of more than 10% from conventional Ta/Ru/Ta buffer layer.The CoFeB layer blocks increased roughness from carrying from the bottomcontact into the MTJ film stack.

Additionally, replacing Ru with Ir in the SyF coupling layer and cappinglayer also has demonstrated an increase in the TMR (%) even afterannealing at temperatures up to 450° C. Some embodiments implementing anIr containing SyF coupling layer show a TMR (%) improvement of more than10% from conventional Ru containing SyF coupling layer. Moreover, byeliminating Ru in the SyF coupling layer and the capping layer, the filmTMR is enhanced by eliminating Ru diffusion towards the MgO. It islikely that the higher thermal stability of IrO₂ than RuO₄ plays a rolein eliminating diffusion.

Configurations such as those of FIGS. 2A-2C provide advantages overconventional film stacks. The first advantage is the buffer staysamorphous even with high temperature thermal process and blocks thetexture from the bottom contact. The second advantage is the strongantiparallel coupling between the pinning layers brought by Ir. Thethird advantage is the TMR improvement by using the new buffer layer andremoving Ru from the stack. These advantages lead to higher MTJperformance (such as high TMR, high SyF coupling, high perpendicularmagnetic anisotropy of pinned layers and reference layer, andcontrollable perpendicular magnetic anisotropy of free layer) andimproved manufacturability. The MTJ film stack can be used to fabricatememory cells for STT-MRAM application as well as other memory and logicdevices that use MTJs as the unit building block. Physical vapordeposition systems (such as ENDURA® STT MRAM) can be used to deposit theMTJ film stack for high performance STT-MRAM chips. As described herein,the MTJ film stack capable of sustaining high temperature thermalprocess improves both electrical and magnetic properties of the MTJs.

Table 1 and Table 2 show exemplary compositions for film stacks utilizedto form a magnetic tunnel junction (MTJ) structure on a substrate.Materials, compositions, and thicknesses for hard mask layer and bottomcontact layer are known to persons of ordinary skill in the art.

An additional (and optional) Ir and/or Ru layer within the cappinglayer, as described above (represented by 250 x), may be placed on topof the oxygen containing layer. The thickness of this layer may bebetween about 0 Å to about 30 Å. In some embodiments, the CoFeB layer ofthe capping layer is not used when the additional Ir and/or Ru layer isused.

TABLE 1 Thickness Layer Material Composition (Å) Hard mask — — — Cappinglayer Ir and/or Ru — 0-50 Ta — 0-30 CoFeB B: 10-40%, 0-50 Fe: 20-60% Irand/or Ru 0-30 MgO — 0-15 Magnetic storage layer CoFeB B: 10-40%, 5-20Fe: 20-60% Ta, Mo, and/or W 0-8 CoFeB B: 10-40%, 5-20 Fe: 20-60% Tunnelbarrier layer MgO — 1-15 Magnetic reference CoFeB B: 10-40%, 5-20 layerFe: 20-60% Structure blocking Ta, Mo, and/or W — 0-8 layer Secondpinning layer Co — 0-10 [Co/Pt]_(p) p: 0-5 Co: 0.5-7; Pt: 0.5-8 SyFcoupling layer Ir or Ru — 3-10 First pinning layer Co — 0-10 [Co/Pt]_(m)m: 3-10 Co: 0.5-7; Pt: 0.5-8 Seed layer Pt, Ir, and/or Ru 0-60 Bufferlayer TaN and/or Ta 0-40 CoFeB B: 10-40%, 0-20 Fe: 20-60% Bottom contact— — —All values for composition and thickness are listed as approximateranges.

TABLE 2 Composition Thickness Layer Material (wt %) (Å) Capping layer Irand/or Ru — 0-50 Ta — 0-30 CoFeB B: 10-40%, 0-50 Fe: 20-60% Ir and/or Ru0-30 MgO — 0-15 Magnetic storage layer CoFeB B: 10-40%, 5-20 Fe: 20-60%Ta, Mo, and/or W 0-8 CoFeB B: 10-40%, 5-20 Fe: 20-60% Tunnel barrierlayer MgO — 1-15 Magnetic reference CoFeB B: 10-40%, 5-20 layer Fe:20-60% Structure blocking Ta, Mo, and/or W — 0-8 layer Second pinninglayer Co — 0-10 [Co/Pt]_(p) p: 0-5 Co: 0.5-7; Pt: 0.5-8 SyF couplinglayer Ir or Ru — 3-10 First pinning layer Co — 0-10 [Co/Ni]_(n) n: 1-10Co: 1-8; Ni: 1-8 Seed layer NiCr — 0-100 Buffer layer CoFeB B: 10-40%,0-20 Fe: 20-60% TaN and/or Ta — 0-40All values for composition and thickness are listed as approximateranges.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present invention without departing from the spirit andscope of the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A film stack, comprising: a buffer layer; asynthetic ferrimagnet (SyF) coupling layer; and a capping layer, whereinthe capping layer comprises one or more layers, and wherein the cappinglayer, the buffer layer, the SyF coupling layer, or a combinationthereof, is not fabricated from Ru.
 2. The film stack of claim 1,further comprising one or more of: a seed layer; or a first pinninglayer; or a second pinning layer; or a structure blocking layer; or amagnetic reference layer; or a tunnel barrier layer; or a magneticstorage layer; or a hard mask.
 3. The film stack of claim 2, wherein:the seed layer is disposed over the buffer layer; or the first pinninglayer is disposed over the seed layer; or the synthetic ferrimagnet(SyF) coupling layer is disposed over the first pinning layer; thesecond pinning layer is disposed over the SyF coupling layer; or thestructure blocking layer is disposed over the second pinning layer; orthe magnetic reference layer is disposed over the structure blockinglayer; or the tunnel barrier layer is disposed over the magneticreference layer; or the magnetic storage layer is disposed over thetunnel barrier layer; or the capping layer is disposed over the magneticstorage layer; or the hard mask is disposed over the capping layer. 4.The film stack of claim 2, wherein the seed layer comprises: (a) a NiCrcontaining layer; or (b) a Pt containing layer, an Ir containing layer,a Ru containing layer, or a combination thereof.
 5. The film stack ofclaim 1, wherein the capping layer comprises an Ir containing layer, aRu containing layer, or a combination thereof.
 6. The film stack ofclaim 1, wherein the capping layer comprises: an oxygen containinglayer.
 7. The film stack of claim 1, wherein the capping layercomprises: a CoFeB containing layer.
 8. The film stack of claim 1,wherein the capping layer comprises: a Ta containing layer.
 9. The filmstack of claim 1, wherein the capping layer comprises: an Ir containinglayer, a Ru containing layer, or a combination thereof as a top layer;and an oxygen containing layer, wherein the top layer is disposeddirectly above the oxygen containing layer.
 10. The film stack of claim1, wherein the capping layer comprises: an Ir containing layer as a toplayer; and a W containing layer, an oxygen containing layer, a second Ircontaining layer disposed directly above the oxygen containing layer, aCoFeB containing layer, a Ta containing layer, a Mo containing layer, ora combination thereof.
 11. The film stack of claim 1, wherein the SyFcoupling layer comprises: an Ir containing layer.
 12. The film stack ofclaim 1, wherein the buffer layer comprises: a CoFeB containing layer.13. The film stack of claim 12, wherein a wt % of boron in the bufferlayer is between about 20 wt % and 40 wt %.
 14. The film stack of claim12, wherein: the seed layer comprises a NiCr containing layer; and thebuffer layer further comprises a TaN containing layer, a Ta containinglayer, or a combination thereof, wherein the CoFeB containing layer ofthe buffer layer is disposed over the TaN containing layer of the bufferlayer, the Ta containing layer of the buffer layer, or a combinationthereof.
 15. The film stack of claim 12, wherein the seed layercomprises a Pt containing layer, an Ir containing layer, a Ru containinglayer, or a combination thereof; and the buffer layer further comprisesa TaN containing layer, a Ta containing layer, or a combination thereof,wherein the CoFeB containing layer of the buffer layer is disposed underthe TaN containing layer of the buffer layer, the Ta containing layer ofthe buffer layer, or a combination thereof.
 16. A film stack,comprising: a buffer layer, wherein the buffer layer comprises a CoFeBcontaining layer; a synthetic ferrimagnet (SyF) coupling layer, the SyFcoupling layer comprising an Ir containing layer; and a capping layer,wherein the capping layer comprising one or more layers, and wherein thecapping layer, the buffer layer, the SyF coupling layer, or acombination thereof, is not fabricated from Ru.
 17. The film stack ofclaim 16, wherein the capping layer comprises: an Ir containing layer asa top layer; and a W containing layer, an oxygen containing layer, asecond Ir containing layer disposed directly above the oxygen containinglayer, a CoFeB containing layer, a Ta containing layer, a Mo containinglayer, or a combination thereof.
 18. The film stack of claim 16, whereinthe buffer layer further comprises a TaN containing layer, a Tacontaining layer, or a combination thereof; and the film stack furthercomprises a seed layer, the seed layer comprising: (a) a NiCr containinglayer; or (b) one or more of a Pt containing layer, an Ir containinglayer, a Ru containing layer, or a combination thereof.
 19. A filmstack, comprising: a buffer layer, wherein the buffer layer comprises aCoFeB containing layer, wherein a wt % of boron is greater than about20%; a synthetic ferrimagnet (SyF) coupling layer, the SyF couplinglayer comprising an Ir containing layer; and a capping layer, whereinthe capping layer comprises one or more layers, wherein a top layer ofthe capping layer is an Ir containing layer, and wherein the cappinglayer, the buffer layer, the SyF coupling layer, or a combinationthereof, is not fabricated from Ru.
 20. The film stack of claim 19further comprising: a seed layer, the seed layer comprising: (a) a NiCrcontaining layer; or (b) a Pt containing layer, an Ir containing layer,a Ru containing layer, or a combination thereof; and the buffer layerfurther comprises a Ta containing layer, a TaN containing layer, or acombination thereof.